Diana Wallis studied history at North London Polytechnic and graduated as a BA in 1975. She obtained a Master of Arts (MA) degree from the University of Kent in 1976. In 1984, Walis received a Certificate of aptitude for the profession of solicitor. Between 1984 and 1999 she worked as a solicitor in London and Hull.
In 1999 Diana Wallis was elected member of the European Parliament and remained an MEP until 2012. During that time she was member of the Group of the European Liberal, Democrat and Reform Party, member of the Group of the Alliance of Liberals and Democrats for Europe, Chair of the Delegation for relations with Switzerland, Iceland and Norway and to the European Economic Area (EEA) Joint Parliamentary Committee, Vice-Chair of the Delegation for relations with Switzerland, Iceland and Norway, Vice-President of the European Parliament, Vice-President of the Parliament's Bureau, member of the Committee on Legal Affairs and the Internal Market, member of the Temporary committee on human genetics and other new technologies in modern medicine, member of the Delegation to the European Economic Area Joint Parliamentary Committee (EEA), member of the Committee on Petitions, member of the Committee on Legal Affairs, member of the Delegation for relations with Switzerland, Iceland and Norway and to the European Economic Area (EEA) Joint Parliamentary Committee, member of the Conference of Delegation Chairs, member of the Committee of Inquiry into the crisis of the Equitable Life Assurance Society, member of the Committee on Petitions, member of the Parliament's Bureau and member of the Delegation for relations with Switzerland and Norway and to the EU-Iceland Joint Parliamentary Committee and the European Economic Area (EEA) Joint Parliamentary Committee.